1. Field of the Invention
The present invention relates to a method of reproducing a recording medium and an apparatus for reproducing a recording medium. More particularly, to a method of and an apparatus for reproducing a recording medium on which data is recorded discretely.
2. Background of the Invention
As recording media for recording music information, audio signals, and general data thereon, there are disk-shaped recording media in addition to tape-shaped recording media such as a magnetic tape. Some of the disk-shaped recording media are magnetic disks such as a floppy disk and optical discs such as a magneto-optical disc on which data can be recorded optically. In the case of the magneto-optical disc, it is possible to repeatedly erase or rewrite data once recorded on the disc and the disc has a capacity of recording a greater amount of data as compared with the magnetic disk. By way of example, a case where a magneto-optical disc is used as the recording medium and an audio signal or music information is recorded on and reproduced from the magneto-optical disc will be described below.
FIG. 1 shows an example of a format of a magneto-optical disc D as a disk-shaped recording medium on which data can be recorded. On a magneto-optical disc D shown in FIG. 1, there are provided a lead-in area on the side of the inner circumference of the disc and a lead-out area on the side of the outer circumference of the disc. The area provided between the lead-in area and the lead-out area on the magneto-optical disc D constitutes a data-recording area in which data is actually recorded. At a portion of the data-recording area close to the lead-in area, there is provided a TOC (Table Of Contents) area. In this T0C area, there are recorded the total recording time of data or programs recorded in the data-recording area of the magneto-optical disc D, the total number of data or the total number of programs, start addresses and end addresses of the data or programs, title information such as titles of pieces of music, and information indicative of connective relationships between parts, as small recording areas, to be described later. The TOC area has a first TOC area having information, not rewritable, recorded therein when the magneto-optical disc is fabricated and a user-TOC area as a second TOC area having therein recorded information which is rewritable by the user. As shown in FIG. 1, there are recorded start addresses and end addresses for six programs in the second TOC area of the magneto-optical disc D. For example, there are recorded the start address A and end address B of the program number 1, the start address C and end address D of the program number 2,and so on through the start address K and end address L of the program number 6.
As shown in FIG. 2, the magneto-optical disc D is provided with a pregroove G previously formed in one side of the disc substrate Sd of the magneto-optical disc D. The pregroove G is arranged to be wobbling at a cycle of 1/(21.05 KHz to 23.05 KHz) in the radial direction of the magneto-optical disc D. Address data can be recorded along the whole circumference of the magneto-optical disc by wobbling the pregroove G in the radial direction of the disc in accordance with FM-modulated address information. A spot SP of a light beam emitted from an optical head is adapted to travel along the pregroove G, relatively to the magneto-optical disc D.
FIG. 3 shows a detailed record format of the magneto-optical disc D. Basically, recording of data on the magneto-optical disc D and reading of data recorded on the magneto-optical disc D are performed in units of a called cluster. Each cluster is formed of 32 data sectors, in which data are recorded, and 4 linking sectors disposed on the forward side of the data sectors. Of the 4 linking sectors, 3 sectors L at the head are provided for the purpose of preventing interleave interference from occurring between adjoining clusters and 1 sector S following them is provided for recording subcode data therein. The sectors are formed of a plurality of sound groups, i.e., 2 sectors are formed of 11 sound groups. In this example, 1 sector is formed of 2352 bytes, of which 2332 bytes are for data. One sound group is formed of 424 bytes. Further, one sound group includes 512 samples of audio signals for the right channel and left channel, which corresponds to the reproducing time 11.61 msec.
In the case of the present magneto-optical disc D, the data recorded on the disc can be erased or rewritten, and therefore, it is possible to edit data previously recorded thereon and make various data into one set of data. For example, six programs from program number 1 to program number 6 are recorded on the magneto-optical disc D as shown in FIG. 1. Suppose that the program number 3 is erased from them. This erasing operation can be carried out not only by actually erasing the data in the data-recording area from the start address E to the end address F, but also by erasing the data related to the program number 3 in the second TOC area. In this example, referring to FIG. 4, if the data related to the program number 3 in the second TOC area is rewritten to blank data, the program number 3 is considered to have been erased. At the same time, the program numbers 4, 5, and 6 existent so far are sequentially changed to new program numbers 3, 4, and 5 as shown in FIG. 4.
FIG. 5 shows an example where two sets of data are combined into one set of data. In FIG. 5 is shown a case where programs which have so far been the program numbers 4 and 5 are changed to a new program number 4 in the second TOC area. In this case, with the change in the program number, the start address is set to G and the end address is set to J. At the same time, the program which has so far been the program number 6 is changed to a new program number 5. In this way, programs can be erased and edited at will in the magneto-optical disc D.
While it is possible to erase and edit previously recorded data and programs on the magneto-optical disc D according to user needs as described above, if data or a program is recorded anew after the above described erase or edition has been made, such data can not always be recorded continuously in the data-recording area of the magneto-optical disc D. The reason why is because the area which can be used for recording data becomes discontinuous, or discrete, by the erasing processing as described in FIG. 4 and FIG. 5. This will be described more particularly with reference to FIG. 6. When a program with a program number 6 is newly recorded, one set of program (data) comes to be recorded in a plurality of small recording areas. The small recording area will hereinafter be called "part P". In the example shown in FIG. 6, the program number 6 is newly recorded divided in four parts from the part P(6-1) to part P(6-4). The information indicative of the connective relationships from the part P(6-1) to the part 6(P-4) is recorded in the second TOC area. When the program number 6 is reproduced, the data recorded in the areas from the part P(6-1) to the part P(6-4) are sequentially read in accordance with the information about connections recorded in the second TOC area.
A case where the magneto-optical disc D with data recorded as described above is reproduced at high speed will be described below with reference to FIG. 7(A) and FIG. 7(B). The phase high speed reproducing operation is herein used to refer to an operation to partially reproduce and output the data recorded in the data-recording area during a searching operation of a plurality of sets of data and programs recorded on the magneto-optical disc D. In the high-speed reproduction, such an operation for example is repeated as, after the light beam emitted from an optical head was caused to jump over 10 tracks of the magneto-optical disc D, to have data in four sectors reproduced as shown in FIG. 7(A).
When one set of program or data is recorded within one part, satisfactory results will be obtained by simply repeating the high-speed reproducing operation. However, when one program is discretely recorded in a plurality of parts P, it becomes necessary, after finishing high-speed reproduction of a preceding part P, to access the subsequent part P which is in a connective relationship with the preceding part P. When subsequent part P is accessed high-speed reproduction of this subsequent part P can be performed. A state of such high-speed reproduction is shown in FIG. 7(B).
While high-speed reproduction of the part P(6-1), for example, is being performed, if the reproducing point as a result of a 10-track jump gets out of the part P(6-1), then the part P(6-2) subsequent to the part P(6-1) is searched for. When the light beam emitted from the optical head gets inside the range of a part P(6-2) after repetition of accessing operations, it now makes a track jump in the backward direction, and if it then gets out of the part P(6-2), it makes a forward jump again. Through repetition of such operations, it finally locates the starting point, i.e., the start address, of the part P(6-2). Then, the operation to reproduce four sectors from the start point of the part P(6-2) and make the 10-track jump (i.e. high-speed reproduction) is performed for in the part P(6-2).
In this way, the high-speed reproducing operation as shown in FIG. 7(B), when the reproducing point by the light beam emitted from the optical head has got out of a specific part P, it will search for the point corresponding to the start address of the subsequent part P and the high-speed reproduction is started again when the searched start address of the subsequent part P is located. This search can take a long time. In the worst case, reproduced sound the output from the apparatus is broken during the reproduction due ti delay caused by the searching operation.